Structural Order Boosts Spin Polarization and Chiral Enhancement in MOF Catalysts for Oxygen Evolution Reaction

The efficiency of Electrochemical Water Splitting can be improved using chiral catalysts and the Chiral Induced Spin Selectivity (CISS) effect. The spin polarized currents generated by CISS favour the formation of O 2 in its triplet ground state and lower the overpotential required to drive the Oxygen Evolution Reaction (OER). However, systematic studies in classes of closely related materials are lacking. Here, we investigate three pairs of nickel(II) coordination polymers based on 1,4-benzenedicarboxylate ligands with either chiral or achiral alkoxy side chains and three different degrees of crystallinity. The most crystalline materials are authenticated as 2D Metal-Organic Frameworks (MOFs) with a layered structure and hexanickel(II) metallacrown subunits. These noble metal-free compounds serve as efficient catalysts of OER, with current densities that compete with or even largely surpass that of state-of-the-art IrO 2 . All chiral materials show asymmetric spin polarization and improved catalytic activity compared to their achiral counterparts. Crystallinity is found to largely enhance the effect of chirality, although the most crystalline MOF samples retain only ~25% of intact alkoxy groups. Our results establish a correlation between structure, spin polarization, and chiral catalytic enhancement and prove that structural long-range order is more important than the number of chiral centers.